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          <h2 class="post-title" itemprop="name headline">《剑指offer》刷题笔记系列综述</h2>
        

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<ul>
<li><strong>转载请注明作者和出处：<a href="http://blog.csdn.net/u011475210" target="_blank" rel="noopener">http://blog.csdn.net/u011475210</a></strong></li>
<li><strong>代码地址：<a href="https://github.com/WordZzzz/CodingInterviewChinese2" target="_blank" rel="noopener">https://github.com/WordZzzz/CodingInterviewChinese2</a></strong></li>
<li><strong>文章地址：<a href="https://github.com/WordZzzz/Note/tree/master/AtOffer" target="_blank" rel="noopener">https://github.com/WordZzzz/Note/tree/master/AtOffer</a></strong></li>
<li><strong>刷题平台：<a href="https://www.nowcoder.com/" target="_blank" rel="noopener">https://www.nowcoder.com/</a></strong></li>
<li><strong>题&emsp;&emsp;库：剑指offer</strong></li>
<li><strong>编&emsp;&emsp;者：WordZzzz</strong></li>
</ul>
<hr>
<h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>&emsp;&emsp;WordZzzz原计划按照牛客网上面的《剑指offer》的通过率高低来把66道编程题刷一遍，但是后来发现，相对于牛客网上大神的解答，WordZzzz更倾向于原书作者的详解。所以，从今天开始，本博主打算按照《剑指offer》纪念版上的题目顺序来进行后续的总结，以作者何大大思路为主，以牛客网上各路大声的代码为辅，对每一道题的解法进行详细的记录，方便自己日后查看，也为订阅本专栏的各位可爱的亲人们提供一些参考。</p>
<ul>
<li>《剑指offer》何大大的源码（含测试代码）传送门：<a href="https://github.com/zhedahht/CodingInterviewChinese2" target="_blank" rel="noopener">https://github.com/zhedahht/CodingInterviewChinese2</a></li>
<li>当然我自己也fork了一下：<a href="https://github.com/WordZzzz/CodingInterviewChinese2" target="_blank" rel="noopener">https://github.com/WordZzzz/CodingInterviewChinese2</a></li>
<li>再来个码云的传送门吧：<a href="https://gitee.com/WordZzzz/CodingInterviewChinese2" target="_blank" rel="noopener">https://gitee.com/WordZzzz/CodingInterviewChinese2</a></li>
<li>至于《剑指offer》纪念版的电子版当然我也有，网上最清晰的资源，需要的请私信我。有条件的还是建议购买正版书籍，支持何大大，支持正版！</li>
</ul>
<p>&emsp;&emsp;另外，下面这道开胃菜牛客上没有，所以先贴出来了。</p>
<h2 id="赋值运算符函数"><a href="#赋值运算符函数" class="headerlink" title="赋值运算符函数"></a>赋值运算符函数</h2><p>&emsp;&emsp;如下为类型CMyString的生命，请为该类型添加赋值运算符函数。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CMyString</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    CMyString(<span class="keyword">char</span>* pData = <span class="literal">NULL</span>);</span><br><span class="line">    CMyString(<span class="keyword">char</span>* CMyString&amp; str);</span><br><span class="line">    ~CMyString(<span class="keyword">void</span>);</span><br><span class="line">    </span><br><span class="line"><span class="keyword">private</span>:</span><br><span class="line">    <span class="keyword">char</span>* m_pData;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CMyString</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    CMyString(<span class="keyword">char</span>* pData = <span class="literal">NULL</span>);</span><br><span class="line">    CMyString(<span class="keyword">char</span>* CMyString&amp; str);</span><br><span class="line">    ~CMyString(<span class="keyword">void</span>);</span><br><span class="line">    </span><br><span class="line"><span class="keyword">private</span>:</span><br><span class="line">    <span class="keyword">char</span>* m_pData;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>
<h3 id="考察细节"><a href="#考察细节" class="headerlink" title="考察细节"></a>考察细节</h3><ul>
<li>是否会把返回值的类型声明为该类型的引用，并在函数结束前返回实例自身的引用（即*this）。只有返回一个引用，才可以允许连续赋值。否则如果函数的返回值是void，应用该赋值运算符将不能做连续赋值。假设有3个CMyString的对象：str1、str2和str3，在程序中语句str1=str2=str3是不能通过编译的。</li>
<li>是否把传入的参数的类型声明为常量引用。如果传入的参数不是引用而是实例，那么从形参到实参会调用一次复制构造函数，吧参数声明为引用可以避免这样的消耗，能提高代码的效率。同时，我们在赋值运算符函数中不会改变传入的实例的状态，因此应该为传入的引用参数加上const关键字。</li>
<li>是否释放实例自身已有的内存。如果我们忘记在分配新内存之前释放自身已有的空间，程序将出现内存泄漏。</li>
<li>是否判断传入的参数和但钱的实例是不是同一个实例。如果是同一个，则不进行赋值操作，直接返回。如果事先不判断就进行赋值，那么在释放自身的内存的时候就会导致严重的问题：当*this和传入的参数是同一个实例时，那么一旦释放了自身的内存，传入的参数的内存也同时被释放了，因此再也找不到需要赋值的内容了。</li>
</ul>
<h3 id="经典的解法"><a href="#经典的解法" class="headerlink" title="经典的解法"></a>经典的解法</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">CMyString&amp; CMyString::<span class="keyword">operator</span> = (<span class="keyword">const</span> CMyString &amp;str)</span><br><span class="line">&#123;</span><br><span class="line">    <span class="keyword">if</span>(<span class="keyword">this</span> == &amp;str)</span><br><span class="line">        <span class="keyword">return</span> *<span class="keyword">this</span>;</span><br><span class="line">    <span class="keyword">delete</span> []m_pData;</span><br><span class="line">    m_pData = <span class="literal">NULL</span>;</span><br><span class="line">    m_pData = <span class="keyword">new</span> <span class="keyword">char</span>[<span class="built_in">strlen</span>(str.m_pData) + <span class="number">1</span>];</span><br><span class="line">    <span class="built_in">strcpy</span>(m_pData, str.m_pData);</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">return</span> *<span class="keyword">this</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>&emsp;&emsp;这是一般教材上提供的参考代码。明眼人可能会发现，上述代码在分配内存之前先用delete释放了实例m_pData的内存。如果此时内存不足导致new char抛出异常，m_pData将是一个空指针，这昂非常容易导致程序的崩溃。</p>
<h3 id="考虑异常安全性的解法"><a href="#考虑异常安全性的解法" class="headerlink" title="考虑异常安全性的解法"></a>考虑异常安全性的解法</h3><p>&emsp;&emsp;要想在赋值运算符函数中实现异常安全性，一般有两种方法。一个简单的办法是我们先用new分配新内存再用delete释放已有的内容；一个更好的方法是创建临时实例，再交换临时实例和原来的实例。参考代码如下：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">CMyString&amp; CMyString::<span class="keyword">operator</span> = (<span class="keyword">const</span> CMyString &amp;str)</span><br><span class="line">&#123;</span><br><span class="line">    <span class="keyword">if</span>(<span class="keyword">this</span> != &amp;str)</span><br><span class="line">    &#123;</span><br><span class="line">        CMyString strTemp(str);</span><br><span class="line">        </span><br><span class="line">        cahr* pTemp = strTemp.m_pData;</span><br><span class="line">        strTemp.m_pData = m_pData;</span><br><span class="line">        m_pData = pTemp;</span><br><span class="line">    &#125;</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">return</span> *<span class="keyword">this</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>&emsp;&emsp;程序比较简单，值得注意的是，strTemp是一个局部变量，程序运行到if的外面的时候，也就出了该变量的作用域，就会自动调用其析构函数，把strTemp.m_pData所指向的内存释放掉。由于strTemp.m_pData指向的内存就是实例之前m_pData的内存，这就相当于自动调用析构函数释放实例的内存。</p>
<p><strong><font color="red" size="3" face="仿宋">系列教程持续发布中，欢迎订阅、关注、收藏、评论、点赞哦～～(￣▽￣～)～</font></strong></p>
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